1. Field of the Invention
The invention relates to an apparatus and method for programming and operating a machine tool, particularly relating to, but not limited to, drilling printed circuit boards for electronic components.
2. Prior Art
Several approaches are used to drill holes in work pieces, such as printed circuit boards. For large quantities, fully automatic drilling equipment with precise mechanical components and numerical control techniques are used. To obtain the desired accuracy, high precision bearings, lead screws, etc. are used in a rigid and costly structure. This equipment uses a sophisticated control system and considerable time and skill are required to programme and maintain such devices.
For smaller quantities a single manual drill is commonly used in which an operator moves the work piece by hand, visually aligns the work piece with respect to a drill bit, and causes the drill bit to penetrate the work piece. Accurate work piece/drill bit alignment is assisted by an optical device which magnifies the hole position pattern imprinted on the work piece, or by a stylus that senses a hole in a template attached to the work piece. For use with the stylus, normally the operator first makes a template of the holes to be drilled in the work piece by using an optical magnifier for greater accuracy. The template is attached to the work piece and positioned under the stylus so that the stylus rests lightly on the template surface. As the template is moved relative to the stylus, when the stylus comes sufficiently close to a hole, it drops into it and a solenoid, air cylinder or other means forces the stylus down into the hole. The downward force moves the loosely held work piece and template into accurate alignment with the drill bit and simultaneously clamps the work piece flat to the drill table so that clean, accurate holes can be drilled. When the stylus has accurately positioned and clamped the work piece, a switch is actuated to commence drilling. For somewhat higher production rates, a quad drill can be used in which a drilled template is clamped to a work table and a self-centering stylus is aligned with the holes. Four drill bits are mechanically linked to the stylus to follow movement thereof and to drill simultaneously four stacks of boards clamped on the table. Some problems associated with these two manual methods relate to relatively low production rates, operator fatigue and operator error.